Webbird, you are entering an area where we have done a lot of guesswork, and CA is no help to us. It appears to me that rebel definition is rather fluid. You can make faction_creator and default faction different, as well as add rebel units to the rebels defined for the province that are different in culture/faction from either of the above. There appears to be no set rule for this. The name of the general of any starting rebel garrison must match the names list of the sub faction, but other than that it seems like you can come up with any number of combinations.